Thermal switch



E, BLE I'Z THERMAL SWITCH Jan. 15, 1935.

Filed Oct. 6, 1933 INVENTOR Edward B/e 72 ATTORNEY S E & E N H W Patented Jan. 15, 1935 THERMAL SWITCH Edward Bletz, Lexington, Ohio, assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa; a corporation of Pennsylvania Application October 6, 1933, Serial No. 692,495

4 Claims.

My invention relates to thermostatic switches and more particularly to thermostatic temperature-limiting devices.

An object of my invention is to provide a relatively simple and compact temperature-limiting switch for an electrical energy-translating device.

Another object of my invention is to provide a snap acting thermal control switch operatively associated with an electrical energy translating device to limit the temperature rise thereof and to prevent reenergization of the energy-translating device under all normal temperature conditions. Another object of my invention is to provide a device that shall embody a snap acting bimetal disc which is thermally actuable to circuit interrupting position and is manually reclosable.

Other objects of my invention will either be self evident from the description of the device and its operation or will be hereinafter pointed out.

In practicing my invention, I provide a snap acting bimetal disc adapted to be mounted in heat receiving relation to an electric energy translating device and to control the energizing circuit thereof, which bimetal disc is adapted to be actuated from its circuit-closing to its circuitopening position at a predetermined maximum temperature of the energy-translating device and of the bimetal member and which remains in its open position irrespective of the return of the temperature of the energy-translating device to its original value, and must be reclosed manually.

In the single sheet of drawings,

Figure 1 is a view in end elevation of an electric motor with which the device embodying my invention may be associated to be controlled thereby,

Fig. 2 is a view in section through the device embodying my invention, and

Fig. 3 is a view similar to that of Fig. 2 of a modified form of device embodying my invention.

In the operation of energy-translating devices such as motors, it may be desirable or necessary to control the energizing circuit of the device in such manner as to disconnect the device from the energizing circuit when any part thereof reaches a predetermined maximum temperature value, which maximum is usually determined by the type and grade of electric-insulating material used in the device, the circuit not being reclosable irrespective of the return of the energy translating device to its initial temperature, which may be that of the ambient atmosphere. The device embodying my invention provides such a means and while I propose to illustrate it when utilized in cooperation with an electric motor, I 5

desire it to be understood that its use is not limited to a motor and that it may be used in cooperation with other forms of energy-translating devices and that it is operative not only in combination with a device experiencing a rise 10 of temperature, but also when used with a device or system experiencing a drop in temperature, such as a refrigerating system.

I have illustrated in Fig. 1 of the drawing a motor assembly designated generally by the nu- 15 meral 11 and while not specifically shown, it is to be understood that the assembly includes in addition to the motor housing 13, a stator and a stator winding therein as well as a rotor which latter is indicated generally by the rotor shaft 15. The leads of the motor 11 are indicated at 17 and 19, respectively, and it is to be noted that the thermostatic switch particularly embodying my invention and designated by numeral 21 is mounted in heat-transferring relation to and on the casing 13 and that it is connected in series circuit relation with the energizing winding of the motor.

Referring now to Fig. 2 of the drawing, I have there illustrated the thermostatic switch structure 21 as including a relatively shallow housing 23 having flanges or ears 25 at each end or side thereof, the casing 23 being of substantially dished shape and of such inner contour as to fit closely against the outer surface of casing 13.

A sheet or disc 27 of electric-insulating material such as mica, is located against the inner surface of dished member 23 and a plurality of fixed contact members 29 are secured against the outer surface of disc 27 in a manner well known in the art.

A snap acting disc 31 of the kind disclosed and claimed in Patent No. 1,448,240 to J. A. Spencer is supported at its central portion on an adjustably mounted stud 33. A plurality of movable contact members 35 are insulatedly supported adjacent to the peripheral portion of bimetal disc 31 and cooperate with fixed contact members 29 to control an electric circuit including in this particular instance, the energizing winding of motor 13. The terminals and terminal leads of the thermostatic switch 21 are indicated generally only, as any desired construction effective for the intended purpose may be used.

The stud 33 is adjustably mounted in a metal bushing 3'7, the two members being provided with cooperating external and internal screw threads to permit of moving stud 33 axially of its length;

as by means of an adjusting lever 39 secured to the outer end of stud 33. The stud 33 is normally held in a fixed position by means of a small pin 41 fitting into stud 33 and adapted to engage a lug or extension 43 of bushing 3'7 which bushing is suitably secured to the member 23 in any well known manner as by rounding over the inner edge or end. In order to hold stud 33 in such position that pin 41 shall engage lug 43, I provide a spring 45 having one end fitting into a hole in casing 23 and its other end engaging pin 41 to yieldingly tend to turn stud 33 in such direction that members 41 and 43 shall normally be in operative engagement.

Referring now to Fig. 3 of the drawing, I have there illustrated a dished casing 51 which is the counterpart of casing 23 of Fig. 2 and have illustrated a cross bar 53 therein which may be of metal and on which is located a sheet 55 of mica to insulatedly support a fixed contact member 5'7.-

A bimetal disc 59 is supported by annular members 61 on the inside of the peripheral walls of casing 51 or the disc 59 maybe supported by a plurality of spaced pairs of pins or lugs. It is to be understood that anydesired mounting for disc 59 may be utilized so long as the disc and par ticularly its central portion is free to move with a snap action from one limiting position to its other limiting position.

A contact member 63 is insulatedly mounted on the disc 59 at its central portion and may cooperate with fixed contact member 5'7 to control an electric circuit.

A bushing 65 is secured to theouter part of casing 51 and an adjustable stud 6'7 may be axially moved in bushing 65 in substantially the same manner as was hereinbefore set forth in connection with stud 33. A spring 69 is adapted to yieldingly hold the stud 6'7 with a stop pin '71 in engagement with a part of bushing 65 from which position the stud 6'7 may be turned by an actuating lever arm '73. Thus, if disc 59 is moved with a snap action tothe position shown by the broken lines in'Fig. 3, it can be manually forced to the' position shown by the full lines by a turning movement of lever arm '73.

Referring now to the device shown particularly in Fig. 2 of the drawing, the bimetal disc 31 is so treated both mechanically and thermally that it will have a very large temperature differential of operation. Thus, if it is desired to protect an electric motor whose maximum operating temperature should not exceed 240 F. in any part thereof, I would so shape and heat treat the disc 31 asto have a temperature differential of operation of about 280 F. In other words, if the disc 31 snaps to its open position at a temperature of 280 F. in order to interrupt the circuit of an energy translating device such as motor 11 of Fig. 1, it would not automatically return to the position shown in Fig. 2 of the drawing until the ambient temperature is reduced to minus 40 F. If it be assumed that the energy-translating device is located in a closed chamber in which the ambient temperature would never fall as low as minus 40 F., it isobvious that the disc 31 would never return to the position shown in Fig. 2 of the drawing.

In order to provide means to effect such return of the disc to its circuit closing position, I have provided in addition to the lever arm 39 whereby the stud 33 may be moved, a plurality of stop pins 40 which extend through the disc 31 through suitable openings therein and have screw threaded engagement with member 33. In order to effect return of disc 31 when it has been actuated by a temperature change, it is only necessary to so turn lever arm 39 as to force the mid or central portion of disc 31 towards the heads of stop pins 40 whereby upon suflicient axial movement of stud 33 and pressure against the central portion of disc 31 by the shoulder at the disc end of stud 33, the disc 31 is caused to reverse its curvature and to return to the position shown in Fig. 2 of the drawing-which is the circuit closing position. It is also obvious that the stud 33 is automatically returned to its initial position as soon as the operator releases the lever arm 39, so that disc 31 is again in its normal position and ready for another operation. 7

Referring to Fig. 3 of the drawing, it is obvious .that a turning movement of lever'arm '73 will the spring 69 causes the stud 6'7 to return to its normal position, the disc 59 being then ready for another operation.

The device embodying my invention thus provides a relatively simple switch assembly operative to open a circuit upon a predetermined change of temperature from the normal temperature of the device with which the switch is associated but which then becomes substantially inoperative as a thermally actuable switch so that it will remain in its actuated position even though the ambient temperature and the temperature of the energy-translating device may return to the initial or normal temperature. The device embodying my invention thus provides an efiective means for" preventing by its own inherent action the reclosing of a supply circuit for an energy-translating device irrespective of ultimate return of the temperature to its normal value and without requiring the use of auxiliary from the spirit and scope thereof and I desire.

therefore, that only such limitations shall be placed thereon as are imposed by the prior art or set forth in the appended claims.

I claim as my invention:

1. A temperature-limiting means for an electric energy-translating device, comprising a base, I

a'fixed contact member on the base, a cooperating movable contact member, asnap-acting bimetal disc supporting the movable contact member and having a greater temperature differential of operation than that to which it is to be subjected, a stud supporting the disc and having screw-threaded engagement with the base, an arm on the stud for turning .the same to effect operation of the disc in one .direction only and a spring for returning the stud to its initial position after movement thereof by the arm.

2. A temperature-limiting means for an electric energy-translating device located in an ambient medium having a certain normal temperature, said temperature limiting means being adapted to cause deenergization oi the energytranslating device upon a given temperature va-" riation thereof from said normal temperature and including a snap-acting bimetal disc and normally engaged relatively movable contact members actuated thereby, said disc being adapted to cause disengagement of the contact members upon said given temperature variation from the normal value and to hold them disengaged upon return of the temperature to normal value, a base for supporting certain of the contact members, manually actuable means engaging the bimetal disc to cause it to move to contact-engaging position, and resilient means to cause return ot the manually actuable means to its normal position.

3. A temperature-limiting switch for an en-' second contact member, a stud carrying the disc at one of its ends and supported by the base, an actuating lever arm on the other end of the stud to turn the same to vary the position of the disc relatively to the base, and a spring having its ends connected to the base and the stud to return the stud to its normal position after having been turned therefrom.

4. A'temperature-limiting switch for an energy-translating device, including a base, a contact member thereon, a second contact member cooperating with the first contact member to control the circuit 01' the energy-translating device, a. snap-acting bimetal disc actuating said second contact member and having an initial circuit-closing position and an actuated circuitopening position to which it moves by thermal action thereon, manually actuated means to shift the position of a part of the disc to cause it to return to its circuit-closing position after having been actuated thermally, and means for automatically returning the manually actuated means and the part of the disc to their initial positions.

. EDWARD BLETZ. 

